This invention relates to dynamo electric motor structures and more particularly to rotary and linear permanent magnet motors.
Conventional electric motors rely on the interaction of magnetic fields to produce a force which results either rotary or linear motion. The magnetic fields in conventional electric motors providing rotary power are generated by passing an externally provided electric current through conductors in either a stator (i.e. stationary portion of the motor), a rotor (i.e. rotary portion) or both the stator and the rotor. The rotary power of the motor arises from a rotating magnetic field which is created by commutating the electric current, either by a switching the current through different conductors, as in a direct current motor or by a polarity reversal of the electric current as in an alternating current motor.
It is well known that a class of materials known as ferromagnetic materials are also capable of generating a magnetic field having once been energized. Ferromagnetic materials with high coercivity are known as permanent magnets. Permanent magnets are capable of storing a finite amount of energy and retaining the ability to generate a substantial magnetic field until the stored energy is depleted.
There are electric motors that use permanent magnets in either the stator portion of the motor or the rotor portion of the motor. These motors achieve a small size for the amount of power delivered by the motor because the motors avoid having current carrying conductors to produce the magnetic field which is otherwise produced by the permanent magnets. However, these conventional permanent magnet motors still require a source of external power to produce a rotating magnetic field.
There have also been developed permanent magnet motors which use permanent magnets for both the stator and the rotor. For example, U.S. Pat. No. 4,598,221 discloses a permanent magnet motor which relies on an external source of power to rotate the magnetic fields of a rotor by ninety degrees with respect to the interacting stator magnetic fields to eliminate the counterproductive magnetic repulsion and attraction between the rotor and the stator magnets. In another example, U.S. Pat. No. 4,882,509 discloses a permanent magnet motor which relies on an external source of power to position a shield which does not permit coupling between the rotor and the stator magnets at times when attraction or repulsion would drag down the strength of the motor.
There are many instances where a motor action is required and no source of external power is available. Accordingly, a motor which relies solely on the energy stored in permanent magnets would be useful.